The present invention relates to image projection systems, and in particular, to image projection systems designed to reduce the effects of ambient light on image quality.
Present color projectors work by modulating, in time and space, three color bands of light: red, green and blue. This modulated light falls upon a screen that diffusely reflects substantially all incident light. These types of diffuse screens appear white in ambient room light since they are designed to reflect all frequencies of light. This means that the darkest xe2x80x9cblackxe2x80x9d that can be presented on this type of screen is limited by the ambient light conditions. This is why the lights are off in movie theaters and dimmed in conference rooms. Rear projection systems project the modulated light on the back of a diffusive display screen. In the same manner, the projected display image competes with ambient light to set contrast and background darkness. Image projection would be greatly enhanced if projection images could be made to appear as natural objects viewed in ambient light. Likewise, the projection environment would be greatly improved if the ambient light levels could be adjusted for reasons independent of a desired contrast of the display.
Therefore, there is a need for a method and system of projection that allows a displayed image to have a contrast and background darkness based on the projected image and not the ambient light levels.
A projector system includes a modified light source and a modified projection screen. The light source uses preselected bands of visible light which are modulated in conventional ways to generate an image. The projection surface of a diffusive projection screen includes a triple bandpass filter with band passes corresponding to the same preselected bands of visible light of the light source. The modulated preselected bands of visible light from the projector pass through the triple bandpass filter and are transmitted back to a viewer as an image when a frame of modulated pixels are projected onto the diffusive screen. Substantially all ambient light impinging on the projector screen save that which corresponds to the pass bands of the triple bandpass filter is adsorbed or blocked.
A rear projector uses a diffusive projection screen which has the triple bandpass filter on the view side of the screen. In this manner, projected light from the modulated preselected bands of visible light impinge on the projection screen forming an image. The image comprising the modulated preselected bands of visible light passes through the triple bandpass filter and is viewed by an observer. The back or front ambient light not in the same frequency bands as the pass bands of the filter is blocked by the filter.
The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention.